ALSA: scarlett2: Zero initialize ret in scarlett2_ag_target_ctl_get()

Clang warns (or errors with CONFIG_WERROR):

  sound/usb/mixer_scarlett2.c:3697:6: error: variable 'err' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
   3697 |         if (private->autogain_updated) {
        |             ^~~~~~~~~~~~~~~~~~~~~~~~~
  sound/usb/mixer_scarlett2.c:3707:9: note: uninitialized use occurs here
   3707 |         return err;
        |                ^~~
  sound/usb/mixer_scarlett2.c:3697:2: note: remove the 'if' if its condition is always true
   3697 |         if (private->autogain_updated) {
        |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  sound/usb/mixer_scarlett2.c:3688:9: note: initialize the variable 'err' to silence this warning
   3688 |         int err;
        |                ^
        |                 = 0
  1 error generated.

Initialize ret to zero to ensure ret is initialized in all paths within
scarlett2_ag_target_ctl_get(), which matches the style of other
functions in this driver.

Fixes: e30ea534 ("ALSA: scarlett2: Add autogain target controls")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Message-ID: <20240419-alsa-scarlett2-fix-wsometimes-uninitialized-v1-1-e2ace8642e08@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett2.c

@@ -3685,7 +3685,7 @@ static int scarlett2_ag_target_ctl_get(
 	struct usb_mixer_elem_info *elem = kctl->private_data;
 	struct usb_mixer_interface *mixer = elem->head.mixer;
 	struct scarlett2_data *private = mixer->private_data;
-	int err;
+	int err = 0;
 
 	mutex_lock(&private->data_mutex);